Pilot signals (or reference signals) are commonly used in data transmissions to allow a receiver to make an estimate of characteristics of a radio channel in which the data is transmitted, allowing improved reception accuracy. For the proposed version of transmission scheme known as Generalized Frequency Division Multiplexing (GFDM), two pilot schemes have been discussed, a preamble technique and a scattered pilot symbol technique with interference pre-cancellation. The preamble technique is based on adding pilot symbols (time division multiplexed symbols that occupy all subcarriers or a significant portion of the carrier bandwidth) as a preamble to a modulated data block. The scattered pilot symbol technique adds pilot symbols (frequency division multiplexed) within a multiplexed data block. Each technique has certain advantages and drawbacks. In particular, the preamble technique allows reuse of known preamble techniques but has the possibility of higher overhead and out of band emissions. The scattered pilot symbol with interference pre-cancellation may provide fairly efficient overhead but may incur a power penalty and additional hardware for high dynamic range between subcarriers. Furthermore, the use of this scheme for multiple antennas is unclear.
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